Spencer Lewis, the headteacher of Yavneh College in Borehamwood, has joined colleagues from local schools in an appeal to parents to discuss the dangers of drug use with their children.
In a joint letter, the heads said they were “very worried about the rise in the use of drugs by young people”.
They warned that there had been an “alarming growth” in the use of such drugs as ketamine and cocaine.
Social media was making it easier for young people to obtain supplies.